Amplifier circuit



v. 25, 1952 R. B. SANGER 2,619,613

AMPLIFIER CIRCUIT Filed May 27, 1950 SIGNAL ,l SOURCE PLATE CURRENT IN TUBE l7 CONTROL-GRID VOLTAGE PLATE CURRENT IN TUBE 22 j; W I W I Fig. 3'

1N VENTOR. RICHARD B. SANGER ATTORNEYS Patented Nov. 25, 1952 omrso STATES eras-r- AMPLHIER CIRCUIT A olicationMar 'l, 1 .S rial N 1 57 3 Claims.

This invention relates to electronic amplifier circuitsxan'd particularly tothe deflection circuits use'd'in cathode-ray oscillographs and similar, instruments.

When it is desired to monitor, television signals; which contain information OYGIIa Wide band 'offrequenciesextending from D. C. to perhaps orfimegaicycles per second; it is necessary that some meansbe providedfor amplifying either the complete-signal, including the D. C. component; or just"the'alternatingcomponents of the signal and restoring the D. C. component in or prior tothelast amplifier stage that a complete signal-may be presented on the face of a cathode-- ray tube. As iswell known, it is desirable that the signal be applied to the deflection plates of the cathode-ray tube through'an amplifier bal- -anced=with respect to a fixed voltage, such as ground, to prevent trapezoidal distortion of'the pattern. A centering circuit must be included in:' the oscillograph to allow the operators to center-th'e pa-ttern or move-it about on the face of the:cathode-ray tube, and this centering circuit mustnottintroduce any distortion into the amplifier.

Accordingly it is an object of the invention to provide an improved cathode-ray oscillograph amplifier;

Another object is to provide-an improved amy piffienfor a. .cathode-ray oscillographused as a television waveform monitor.

Ai'Jfurther-object is to provide an improved D. C. restoration and centering circuit for use in :aLcathodeeray oscillograph used as a television wa-veiormrmonitor;

Further "objects. andadvantages of the invention :will the: apparent after studying the following description.

The invention is embodied in a cathode-ray tube:circuit-employinga pair of amplifier tubes foi applyingvsignals to the cathode-raytube deflection-means an-dadjustable direct current restoration; circuits between ,said tubes to permit symmetrical, applicationqofsaid signals to the c-aethoderray tube. The invention will bemore clearly understood by-reference to the following specification-and drawings in which :Figure lshows a circuit of a cathode-ray oscillograph amplifier embodying the invention.

Figure 2 shows a typical set of control-grid voltage =vs. plate current curves for the final amplifier'tubesinFigurel.

' Figure 3 shows-the pattern on the face of a catlmde-ray oscillograph monitoring a television signal;

'In'Figure 1 a signal source II, which-may be any circuit throughwhich a. television or similar signal passes, is connected to-the input of'an amplifier l2. The output signal, of the amplifier l2 isthen fedto a, second amplifier l3 connected as a cathode follower, which in turn'is' connected through line I4, condenser l5 and line I6 to output amplifier I1. Also amplifier I3 is connected through a condenserl8, to a, polarity inverting amplifier I9. The output signal ofi'the amplifier I9 is connected through condenser 20 and line 2| to the second output amplifier 22.

That portion of the circuit between the source I I and the condensers I5 and Z0 is a detailed exposition of atypical circuit used for bringing a deflection signal to a cathode-ray tube andmay be replaced by any circuit capable of feeding signals of opposite polarity and sufiicient magnitude to the condensers I5 and 20.

The D. C. restoration circuit for the signal is symmetrical from the condensers I5 and 20 to the cathode-ray tube. Specifically the bias voltage supply 48, with one end grounded at 4|, furnishes through resistor 42 a voltage to variable resistor 43. The latter resistor serves as a potentiometer which is connected between lines I6 and 2! through resistors 44 and 45. Also connected between lines I6 and 2| are diodes 46 and 41, the former having its cathode connected to line I6 and the latter having its plate connected to line 2|. The plate of diode 46 is connected to one end of potentiometer 43 and is brought to ground through the parallel combination of resistor 48 and condenser 49. The cathode of diode 4'! is brought-to'groundthrough the parallel combination of resistor 50 and condenser '51. The cathodes of tubes I! and 2| are connected togetherand grounded'through resistor 52.

Forapplication of the signal developed on each of the amplifier tube plates, which signal in the one caseis the inverse of the other, the plates of the tubes are connectedto the deflection plates of the cathode ray tube 53, which receive their voltage supply through line 54 which connects thereto through resistors 55 and 55.

tionc-ircuitcomprising the condenser I 5; the (ii-'- .3 ode 46, and the resistor 44. The signal at this point should have the polarity shown by the wave form 60 since this D. C. restoration circuit is connected to restore the negative tips of the voltage to a given level. The negative tips of the wave form 60 are the synchronization pulses of the television wave and are generally more uniform than the positive part which carries the video information.

The output signal of the amplifier I3 is also passed through the polarity inverting amplifier IS in which the plate load is preferably of such a value as to prevent the amplifier 19 from having a gain appreciably greater than unity. The signal from the amplifier l9 has a polarity as shown by the wave form 6 l and the D. C. restoration circuit comprising the condenser 2d, the resistor 45, and the diode 41 restores the positive peaks of the signal 6| to a given value.

The voltage to which the first named D, C. restoration circuit would restore the negative peaks of the signal 60 is the voltage existing at the plate of the diode 46. This'voltage is derived from the bias voltage source by means of voltage divider comprising the resistors 42 and t8 and that part of the potentiometer 43 between the arm and the resistor 48. The voltage to which the positive peaks of the signal would be restored is determined by the voltage on the cathode of the diode 41, which is derived from the voltage across resistor 53 in a manner similar to the voltage across resistor 48.

Figure 2 illustrates the relation between the control grid voltages and the plate currents of the output tubes l1 and 22. These curves are symmetrical about the control grid voltage Eco, which is the voltage between the control grids and the cathodes of the tubes I1 and 22 when the potentiometer s3 is set so that the voltage across resistor 48 is equal to the voltage across resistor 50. This center bias, Eco, is then equal to the voltage across the cathode resistor 52 plus the voltage across resistor 48 (or resistor 50).

It can be seen that as the arm of the potentiometer 43 is rotated toward resistor M, the voltage at the plate of the diode 45 would approach the voltage of the bias supply; although it could never reach that voltage because of the drop of potential across resistor 42. If the bias supply of voltage were positive, the plate of the diode 45 would become more positive and correspondingly the cathode of the diode 47 would become less positive. The effect of this rotation would be to displace the signals 5%) and El to the right on the control-grid voltage axis in Figure 2 without distorting any part of either signal as long as they both remained within the linear portion of the curves of the amplifiers l1 and 22. This linear portion is bounded on the left by the control grid voltage egl to which the upper curve begins to bend and on the right by the voltage eg2 to which the lower curve begins to bend.

Examination of Figure 2 shows that the voltage eg3 to which the signal 60 is restored differs from the voltage g4 to which the signal El is restored. This is necessary in order to make the most economical use of the tubes l1 and 22 since by so doing it is possible to make signals 65! and El have a maximum amplitude and still occupy a minimum space on the curves in Figure 2. If the negative peaks of signal 6!) were restored to the same voltage as the positive peaks of the signal 6|, say Em, the total voltage between the negative tips of the signal 6| and the signal 60 would cover twice the distance along the grid voltage axis of Figure 2 and it would not be possible to change the position of the two signals along this axis within such limits without distorting one signal or the other.

Figure 3 shows a face of a cathode-ray oscillograph tube 53 having a television wave form signal thereon. The marks Ill, H, and 12 represent the white level, blanking level, and synchronizing peak voltage level, respectively. These marks are usually engraved on a screen placed in front of the cathode-ray tube 53 and it is desirable, in checking the operation of the television signal source I I, to position the pattern so that corresponding parts of the television signal lie along side the marks 153, H, and 12. In this way any discrepancy in the television signal may be easily observed.

Although I have illustrated this invention by means of a single example, it will be apparent to those skilled in the art that modifications may be made without departing from the spirit of the invention as illustrated by the following claims.

What I claim is:

1. An amplifier circuit comprising a first and second amplifier tube, each of said tubes having a cathode, anode, and an input electrode, connections to the input electrodes of said tubes to apply thereto oppositely oriented voltage signals; and first and second direct current restoration circuits connected between said signal applying connections, the said restoration circuits comprising a voltage supply, a potentiometer having its movable contact connected to one terminal of said voltage supply; said first restoration circuit comprising a first diode having its cathode connected to the input electrode of said first amplifier tube and its plate connected to one end of said potentiometer, and a resistance capacitance circuit connecting said plate to a second terminal of said voltage supply, said second direct current restoration circuit comprising a diode having its plate connected to the input electrode of said second amplifier and its cathode connected to the other end of said potentiometer,

and a resistance capacitance circuit connectingsaid last-named cathode to said second terminal of said voltage supply.

2. The circuit as defined in claim 1 wherein the output electrodes of said first and second ainplifier tubes are connected to deflection plates of a cathode ray tube.

3. A cathode ray tube amplifier circuit for the application of signals to the deflection plates in the cathode ray tube comprising in combination, a cathode ray tube having deflection means therein, first and second amplifier tubes having an anode, cathode and an input electrode, the anode of each of said tubes being connected to the deflection means of the cathode ray tube, the cathode of each of said tubes being connected to ground through a resistor, and the signal applying and direct current restoring circuits connected to the input'electrodes of each of said tubes, the signal applying circuit of said first am plifier tube, being a coupling condenser connected to preliminary amplification and a signal source for the cathode ray tube, the direct current restorer circuit for said first amplifier comprising a source of voltage connected to a potentiometer, said potentiometer being connected between the signal applying electrodes of the said first and second amplifier tubes, 2, first diode'having its cathode connected to the signal applying electrode of said first amplifier tube and its plate connected to the first side of the said potentiometer, said plate being brought to ground through a resistance capacitance circuit, the signal applying circuit of said second amplifier tube being a coupling condenser connected to said preliminary amplification and a signal source for the cathode ray tube, the direct current restorer for said second amplifier tube comprising a second diode having its plate connected to the signal applying electrode of said second amplifier tube and its cathode connected to the second side of said potentiometer and to ground through a resistance capacitance circuit.

RICHARD B. SANGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

